I. Field of the Invention
The present invention relates to an apparatus for thermosetting thermoplastic tubes in predefined shapes.
II. Description of the Prior Art
Tubes of a thermoplastic material are used in a wide variety of applications, e.g. the automotive industry. In the automotive industry, such thermoplastic tubes are used as fuel conduits for vapor, fuel, hydraulic, cooling and/or oil. In such applications, the tube is oftentimes required to be in a specific shape or configuration prior to its installation in the automotive vehicle.
Previously, in order to form the thermoplastic tube into a specific shape, the thermoplastic tube was inserted into or onto a former which bent the tube into the desired shape. After the tube was inserted into the former and held in the desired shape, it was necessary to heat the thermoplastic material to a temperature at which the thermoplastic material thermally deforms. Following such deformation, the thermoplastic tubes as well as the formers were cooled which causes the thermoplastic to thermally set into the shape defined by the former. Consequently, upon removal of the thermoplastic tube from the former, the thermoplastic tube would retain the shape defined by the former.
There have been several different methods for heating the former with the attached thermoplastic tube. In one previously known method, the formers with the attached thermoplastic tube were inserted into a vat of liquid, typically glycol, which was heated to a temperature at which the thermoplastic material thermally deforms. After immersing the former with the attached thermoplastic tube into the vat for a predetermined period of time, typically several minutes, the former was removed and both the former and thermoplastic tube cooled. This previously known method of heating the thermoplastic tubes, however, had several disadvantages. A primary disadvantage of utilizing a vat of heated liquid is that the overall operation was necessarily messy since liquid from the vat would drip on the workplace around the vat. This, in turn, required that the work area around the vat be continually maintained to ensure safety.
A further disadvantage of this previously known method of heating the formers with the thermoplastic tubing is that it is necessary to periodically dispose of the liquid in the vat. This, in turn, can result in an undesirable environmental impact where materials, such as glycol, are used in the vat.
There have, however, been previously known devices for heating formers with their attached thermoplastic tubes in which the formers were conveyed through a heated oven such as the device disclosed in U.S. Pat. No. 5,200,124 to Bowkett. In this previously known apparatus, a conveyor extended through an oven chamber and the formers were attached to the conveyor so that the conveyor conveyed the formers with their attached thermoplastic tubes through the oven. The oven in turn was heated by radiant heaters in order to heat the thermoplastic tube to a point of thermal deformation. This previously known apparatus, however, has not proven wholly satisfactory in use.
One disadvantage of this previously known apparatus was that the radiant heaters were arranged in the oven so that the radiant heaters concentrated the heat output from the heaters only at the areas of the former at which a bend was desired. This, however, required that the arrangement of the radiant heaters be altered whenever a former with a different shape was conveyed through the oven. Furthermore, this previously known device was inappropriate when formers of different shapes were simultaneously conveyed through the oven.
There have, however, been previously known ovens in which the entire oven chamber was heated to a temperature at which the thermoplastic tube thermally deformed. Radiant heating is typically utilized to heat the interior of the oven. These previously known devices, however, have also not proven wholly satisfactory in use.
A primary disadvantage of these previously known devices is that the entire thermoplastic tube was subject to radiant deformation including not only the bend areas of the former, but also the straight sections of the thermoplastic tube between the bends. The thermal deformation of the straight sections of the thermoplastic tube, however, may actually result in undesirable collapse of the thermoplastic tube. While internal inserts into the thermoplastic tube may be utilized to minimize collapse of the thermoplastic tube due to thermal deformation, the use of such inserts are time consuming, labor intensive and therefore undesirably expensive.
The present invention provides an apparatus for thermosetting thermoplastic tubing which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the apparatus of the present invention comprises an oven having an interior chamber. A conveyor extends through the oven chamber from an inlet end of the oven and to an outlet end of the oven.
The interior of the oven is heated to a temperature approaching that at which the thermoplastic tubing deforms. Preferably, radiant heaters arranged in banks along the interior walls of the oven are utilized to heat the oven chamber.
An elongated former includes a channel dimensioned to receive the thermoplastic tube. Furthermore, this channel has the predefined shape of the desired thermoplastic tube and, as such, includes at least one bend. The thermoplastic tube, furthermore, is sufficiently flexible so that the tube may be inserted into the former channel and thus into the desired final shape for the thermoplastic tube.
Unlike the previously known formers, however, a radiant heat absorbent coating is disposed on the outer surface of the former adjacent to and extending across each bend on the former. This absorbent coating preferably comprises a black coating on the former, such as black paint.
In practice, as the formers with their attached thermoplastic tube are conveyed through the oven interior, the absorbent coating on the former locally increases the heat absorption and heat energy of the tube in the area around the bends of the former in an amount sufficient to reset the elastic memory of the tube at the bend location. In doing so, the absorbent coating relatively quickly heats the bent portions of the thermoplastic tube to a point of thermal deformation. Conversely, the straight sections of the former, i.e. the sections where a bend of the thermoplastic tube is undesired, heat less quickly and also remain at a cooler temperature thus minimizing thermal deformation of the straight sections of the thermoplastic tube and likewise minimizing possible collapse of the thermoplastic tube due to thermal deformation.
After the formers with their attached thermoplastic tubes are conveyed through the oven chamber, the formers and tubes are then cooled in any conventional fashion. After cooling, upon removal of the thermoplastic tube from the former, the thermoplastic tube has thermally set and thus retains the shape of the former.